15_function_basics.ipynb

{
 "cells": [
  {
   "cell_type": "markdown",
   "id": "5e8a7ee3",
   "metadata": {},
   "source": [
    "# Functions-Basics\n",
    "    1. Creating a Function\n",
    "    2. Calling a Function\n",
    "    3. Functions' Arguments \n",
    "    4. keyword Arguments\n",
    "    5. Default Arguments"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "08951367",
   "metadata": {},
   "source": [
    "    A function is a block of code which only runs when it is called.\n",
    "\n",
    "    You can pass data, known as parameters or input arguments, into a function.\n",
    "\n",
    "    A function can return data or None as a result. \n",
    "\n",
    "    The result/output of a function is mainly assigned to a variable ...\n",
    "    "
   ]
  },
  {
   "cell_type": "markdown",
   "id": "510af8e4",
   "metadata": {},
   "source": [
    "    Usecases:\n",
    "    1) Don't Repeat yourself\n",
    "    2) Unit testing"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "473f28b4",
   "metadata": {},
   "source": [
    "## Creating a Function\n",
    "\n",
    "In Python a function is defined using the ‍‍‍`def` keyword:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 7,
   "id": "550bd4e1",
   "metadata": {},
   "outputs": [],
   "source": [
    "#it has no input argument, but has an output\n",
    "def return_func():\n",
    "    return 'hello world'"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "3cb045f5",
   "metadata": {},
   "source": [
    "## Calling a Function\n",
    "\n",
    "To call a function, use the function name followed by parenthesis:"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 9,
   "id": "853d61c9",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'hello world'"
      ]
     },
     "execution_count": 9,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# calling a function\n",
    "return_func()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 10,
   "id": "088c82d7",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "result is: hello world\n"
     ]
    }
   ],
   "source": [
    "# Assigning the output of return_func to a third variable\n",
    "result = return_func()\n",
    "print('result is:', result)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 11,
   "id": "9388d2ff",
   "metadata": {},
   "outputs": [],
   "source": [
    "# a function may have no outputs\n",
    "# In this case, by default, it returns None as its output!\n",
    "def no_return_func():\n",
    "    print('hello world')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 12,
   "id": "9b986d6d",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "hello world\n"
     ]
    }
   ],
   "source": [
    "# call function\n",
    "# It prints 'hello world'. It does not return it!\n",
    "no_return_func()"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 14,
   "id": "1961860a",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "hello world\n",
      "result is: None\n"
     ]
    }
   ],
   "source": [
    "# let's check the return of no_return_func\n",
    "result = no_return_func()\n",
    "print('result is:', result)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "25ebd248",
   "metadata": {},
   "source": [
    "## Function Arguments"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "909b2a68",
   "metadata": {},
   "source": [
    "    Information can be passed into functions as arguments.\n",
    "\n",
    "    Arguments are specified after the function name, inside the parentheses. You can add as many arguments as you want, just separate them with a comma.\n",
    "    \n",
    "    These areguments are called required arguments because they must be provided for the function to work!\n"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 16,
   "id": "33b02292",
   "metadata": {},
   "outputs": [],
   "source": [
    "# a simple function with two parameters\n",
    "def get_power(num, to_power):\n",
    "    return num ** to_power"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 18,
   "id": "3c3014f4",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "result is: 125\n"
     ]
    }
   ],
   "source": [
    "# calling the func function\n",
    "powered_number = get_power(5, 3)\n",
    "print('result is:', powered_number)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "27836552",
   "metadata": {},
   "source": [
    "### If you call the function with less or more than 2 arguments, you will get TypeError!"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 19,
   "id": "bb5f5a2d",
   "metadata": {},
   "outputs": [
    {
     "data": {
      "text/plain": [
       "'pooya mohammadi'"
      ]
     },
     "execution_count": 19,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# These two arguments are not optional!\n",
    "def get_full_name(f_name, l_name):\n",
    "    return f_name + \" \" + l_name\n",
    "\n",
    "get_full_name('pooya', \"mohammadi\")"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 20,
   "id": "48d03378",
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "get_full_name() missing 1 required positional argument: 'l_name'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "Cell \u001b[1;32mIn [20], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[43mget_full_name\u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[38;5;124;43mpooya\u001b[39;49m\u001b[38;5;124;43m'\u001b[39;49m\u001b[43m)\u001b[49m\n",
      "\u001b[1;31mTypeError\u001b[0m: get_full_name() missing 1 required positional argument: 'l_name'"
     ]
    }
   ],
   "source": [
    "get_full_name('pooya')"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 23,
   "id": "cd2d8ba2",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "var_1: 10\n",
      "var_2: 5\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "15"
      ]
     },
     "execution_count": 23,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "def add(var_1, var_2):\n",
    "    print(f'var_1: {var_1}')\n",
    "    print(f'var_2: {var_2}')\n",
    "    return var_1 + var_2\n",
    "add(10, 5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 24,
   "id": "c5e60e7e",
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "add() missing 1 required positional argument: 'var_2'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "Cell \u001b[1;32mIn [24], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[43madd\u001b[49m\u001b[43m(\u001b[49m\u001b[38;5;241;43m10\u001b[39;49m\u001b[43m)\u001b[49m\n",
      "\u001b[1;31mTypeError\u001b[0m: add() missing 1 required positional argument: 'var_2'"
     ]
    }
   ],
   "source": [
    "add(10)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "fe9574d8",
   "metadata": {},
   "source": [
    "### Keyword arguments\n",
    "    The arguments are passed by the name of the input argument defined by the function\n",
    "    The order of arguments is not important, but it's recommanded to maintain the order \n",
    "    of the inputs\n",
    "    It prevents any confusion at the time of argument passing"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 25,
   "id": "3742cbb1",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "var_1: 10\n",
      "var_2: 20\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "30"
      ]
     },
     "execution_count": 25,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# recommended!\n",
    "value = add(var_1=10, var_2=20)\n",
    "value"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 26,
   "id": "04365a32",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "var_1: 10\n",
      "var_2: 20\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "30"
      ]
     },
     "execution_count": 26,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# not recommended!\n",
    "var = add(var_2=20, var_1=10)\n",
    "var"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 27,
   "id": "d2cefe50",
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "add() got an unexpected keyword argument 'var_3'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "Cell \u001b[1;32mIn [27], line 3\u001b[0m\n\u001b[0;32m      1\u001b[0m \u001b[38;5;66;03m# What if providing an argument name which is not defined!\u001b[39;00m\n\u001b[0;32m      2\u001b[0m \u001b[38;5;66;03m# unexpected keyword argument!\u001b[39;00m\n\u001b[1;32m----> 3\u001b[0m \u001b[43madd\u001b[49m\u001b[43m(\u001b[49m\u001b[43mvar_1\u001b[49m\u001b[38;5;241;43m=\u001b[39;49m\u001b[38;5;241;43m20\u001b[39;49m\u001b[43m,\u001b[49m\u001b[43m \u001b[49m\u001b[43mvar_3\u001b[49m\u001b[38;5;241;43m=\u001b[39;49m\u001b[38;5;241;43m10\u001b[39;49m\u001b[43m)\u001b[49m\n",
      "\u001b[1;31mTypeError\u001b[0m: add() got an unexpected keyword argument 'var_3'"
     ]
    }
   ],
   "source": [
    "# What if providing an argument name which is not defined!\n",
    "# unexpected keyword argument!\n",
    "add(var_1=20, var_3=10)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 28,
   "id": "ffe1656f",
   "metadata": {},
   "outputs": [
    {
     "ename": "TypeError",
     "evalue": "add() missing 1 required positional argument: 'var_2'",
     "output_type": "error",
     "traceback": [
      "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
      "\u001b[1;31mTypeError\u001b[0m                                 Traceback (most recent call last)",
      "Cell \u001b[1;32mIn [28], line 1\u001b[0m\n\u001b[1;32m----> 1\u001b[0m \u001b[43madd\u001b[49m\u001b[43m(\u001b[49m\u001b[43mvar_1\u001b[49m\u001b[38;5;241;43m=\u001b[39;49m\u001b[38;5;241;43m20\u001b[39;49m\u001b[43m)\u001b[49m\n",
      "\u001b[1;31mTypeError\u001b[0m: add() missing 1 required positional argument: 'var_2'"
     ]
    }
   ],
   "source": [
    "add(var_1=20)"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "775a8632",
   "metadata": {},
   "source": [
    "### How to combine keyword arguments with positional arguments\n",
    "    positional arguemtns come first\n",
    "    then, keyword arguemtns are used"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 29,
   "id": "4d64f870",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "var_1: 20\n",
      "var_2: 10\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "30"
      ]
     },
     "execution_count": 29,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "var = add(20, var_2=10)\n",
    "var"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 30,
   "id": "44cc4776",
   "metadata": {},
   "outputs": [
    {
     "ename": "SyntaxError",
     "evalue": "positional argument follows keyword argument (2377682373.py, line 2)",
     "output_type": "error",
     "traceback": [
      "\u001b[1;36m  Cell \u001b[1;32mIn [30], line 2\u001b[1;36m\u001b[0m\n\u001b[1;33m    var = add(var_1=20, 10)\u001b[0m\n\u001b[1;37m                          ^\u001b[0m\n\u001b[1;31mSyntaxError\u001b[0m\u001b[1;31m:\u001b[0m positional argument follows keyword argument\n"
     ]
    }
   ],
   "source": [
    "# SyntaxError: positional argument follows keyword argument\n",
    "var = add(var_1=20, 10)\n",
    "var"
   ]
  },
  {
   "cell_type": "markdown",
   "id": "e43f53ce",
   "metadata": {},
   "source": [
    "\n",
    "### Default Parameter/Argument Value\n",
    "\n",
    "    The following example shows how to use a default parameter value.\n",
    "\n",
    "    If the function is called without arguments, it uses the default value if there are any!!\n",
    "    \n",
    "    If you want to have default values, you should specify them after each input argument!\n",
    "    \n",
    "    Default arguments are those that are mainly used by programers or are those that are safer and won't accidentally remove the users' files."
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 31,
   "id": "4b40636f",
   "metadata": {},
   "outputs": [],
   "source": [
    "def add(var_1, var_2=5):\n",
    "    print(f'var_1 is {var_1}')\n",
    "    print(f'var_2 is {var_2}')\n",
    "    return var_1 + var_2"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 32,
   "id": "d8ecd3e7",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "var_1 is 15\n",
      "var_2 is 5\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "20"
      ]
     },
     "execution_count": 32,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# because var_2 is a default parameter, providing the first arg is sufficient!\n",
    "add(var_1=15)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 33,
   "id": "0d5e6e61",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "var_1 is 1\n",
      "var_2 is 15\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "16"
      ]
     },
     "execution_count": 33,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# default arguments' values can be changed\n",
    "add(1, 15)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 34,
   "id": "f66efd6f",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "var_1 is 5\n",
      "var_2 is 4\n"
     ]
    },
    {
     "data": {
      "text/plain": [
       "9"
      ]
     },
     "execution_count": 34,
     "metadata": {},
     "output_type": "execute_result"
    }
   ],
   "source": [
    "# Although the order of input arguments is not required, passing values without order is not recommended.\n",
    "add(var_2=4, var_1=5)"
   ]
  },
  {
   "cell_type": "code",
   "execution_count": 36,
   "id": "131bc961",
   "metadata": {},
   "outputs": [
    {
     "name": "stdout",
     "output_type": "stream",
     "text": [
      "I am from Iran\n",
      "I am from Sweden\n",
      "I am from Turkey\n",
      "I am from Brazil\n"
     ]
    }
   ],
   "source": [
    "# Another example:\n",
    "def my_country(country=\"Iran\"):\n",
    "    print(\"I am from \" + country)\n",
    "\n",
    "my_country()\n",
    "my_country(\"Sweden\")\n",
    "my_country(\"Turkey\")\n",
    "my_country(country=\"Brazil\") "
   ]
  },
  {
   "cell_type": "markdown",
   "id": "f3279850",
   "metadata": {},
   "source": [
    "*_:-)_*"
   ]
  }
 ],
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